OUR DISAPPEARING NATURAL DUNELANDS

Forest and Bird, Volume 15, Issue 3, 1 August 1984, Page 2

OUR DISAPPEARING NATURAL DUNELANDS

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Botanist and Society Member

Shannel Courtney

Our natural dunelands support asmall but fascinating range of native plants and animals. Like many of our remaining natural areas, natural dunelands are threatened as a result of past and present development. Despite this, they are inadequately represented in our reserve system.

"To our left was the open ocean. To our right, mile after mile of low, rounded sandhills ... stretched out as far as we could see ... fringed with Spinifex, Desmoschoenus and other common arenarian plants’. This is an extract from Thomas Cheeseman’s account of the dunes of Northland’s Aupouri Peninsula in 1896. New Zealand has over 100,000 hectares of dune country bordering its coastline and therefore extensive natural dunelands covered with an array of distinctive indigenous species would once have been acommon sight throughout the country. But to many early settlers New Zealand’s dune systems were regarded as sandy wastes — unproductive unless developed. Unfortunately, such attitudes persist even today, and reflect our disregard for the protection of our remaining natural dunelands. They have been reduced to a fraction of their former extent. Together with lowland forests, shrublands, wetlands and tussock grasslands, they join the list of our most threatened habitats. The dune environment The dune environment is one of the most extreme and exacting habitats in New Zealand. This ecosystem supports a small group of highly specialized plants and animals. These species must resist desiccation by unchecked onshore winds, and withstand the burning effects of salt spray. They must cope with large amounts of

drifting sand and constantly struggle against burial and undermining. Plants and animals found here must also tolerate the sand’s high temperatures, high reflectivity, low nutrient status and low capacity to hold water. If this is not enough, the plant species nearest the coast are periodically inundated by seawater during spring tides and storm surges. Dune zonation Atypical dune system has a landward sequence of zones which runs parallel to the coastline. The strand line just above the high tide mark is the first of these zones. It is characterized by a collection of washed up flotsam including driftwood and seaweed. Directly behind the strand is the foredune zone. Here active dune building is occurring. Behind this is a complex system of reardunes which may exceed 100 metres in height and extend up to 4-5 kilometres inland. Interspaced throughout the reardune zone are numerous deflation hollows where sand has been removed down to the watertable. Permanent lakelets may occur here. On the more stable reardunes, vegetation may eventually be succeeded by coastal forest such as the dune podocarp forests of south Westland, the forests at the mouth of the Tahakopa river in the Catlins, and kauri forest on consolidated dunes in Waipoua State Forest. A variety of habitats with their associated fauna and flora adjoin dune systems. These range from coastal turf meadows, estuaries and lagoons, to

swamps (eg Kaimaumau, Northland), red tussock grassland (eg Mason Bay, Stewart Island) and coastal’scrub and forest. Native plants of the dunes The most widespread and successful plants of our natural dunelands are pingao (Demoschoenus spiralis) an endemic sedge and spinifex (S. hirsutus) a grass also native to Australia. Pingao is found from North Cape to Stewart and Chatham Islands. It’s tufted shoots of arched orange-green leaves makes it the most colourful plant of the dunes. Often it can be seen growing sinuously down a dune face. Spinifex occurs throughout the North Island and across the top of the South Island. Its slender network of stems crisscross the dunes, every so often throwing up a sward of silver-haired leaves. Its flowers develop into starlike clusters of ripe fruit which are often seen dispersing their seeds as they blow along the foreshore. Both pingao and Spinifex are true sand binding and dune building plants. Airborne sand is trapped amongst their spreading shoots. They grow upwards so as not to be buried as sand gradually accumulates around them. By this process a dune eventually builds up. Sand sedge, Carex pumila creates dunes in a similar manner although not nearly as effectively. It spreads an open carpet over the moist sand of the strand zone and deflation hollows. Sand convolvulus, Ca/ystegia solanella, with its glossy heart-shaped leaves, and purple-pink trumpet flowers is found mainly on the foredune. There are four other special plants of the foredune and strand line which, although widely scattered throughout New Zealand, have become quite rare. These are the shore milkweed, Euphorbia glauca, which has blue-green fleshy leaves and clusters of red flowers; Pimelea arenaria, the sand daphne; Poa triodioides, a sand tussock; and Theleophyton billardieri, a small mealyleaved herb related to fathen. Two ranunculi also occur on the sandy shore: R. recens, a small, hairy-leaved buttercup; and RA. acaulis, which replants itself by turning the ripe fruit downwards into the sand. One of the rarest plants in the world, Gunnera hamiltonii, of which there is one known wild specimen (a male) spread over

about 30 metres occurs at Mason Bay on Stewart Island at the interface of the reardunes and red tussock grassland and coastal forest. Sand plants of the more stable rear dunes include the low growing, wirystemmed sand coprosma (Coprosma acerosa), the densely tangled pohuehue (Meuhlenbeckia complexa), and the heady smelling tauhinu (Cassinia leptophylla). A curious prostrate broom (Carmichaelia appressa) also occurs on semi-stable dunes, andis totally confined to Kaitorete Spit, near Lake Ellesmere, Canterbury.

These rear dune plants are less able to resist the advance of sand than true sand binders, but are able to produce the root systems necessary to ensure dune stability. The more conspicuous plants of the moist sand hollows include jointed wire rush (Leptocarpus similis) which on its pedestal of roots and old leaf bases, may attain heights exceeding three metres; the northern pampas, (Cortaderia splendens), flax (Phormium tenax), knotted sedge (Scirpus nodosus), and the wire rush, Eleocharis novae-zelandiae. Native animals of the dunes The most diverse group of animals found on our natural dunelands are insects and spiders. Perhaps the best known is the katipo (Latrodectus katipo), one of our most poisonous spiders. Katipo are retiring creatures and may be found in dry places amongst driftwood or the tufts of sandbinding plants. Only the female is poisonous, and produces venom when she is incubating or rearing her offspring. The sand dune hopper with its peculiar sand digging leg paddles, and the sand beetle with multi-speckled coat, are common inhabitants of the strand zone and seaward facing foredunes. They are both likely prey of the carnivorous beach centipede. They may also fall prey to the large native littoral earwig which is particularly common beneath driftwood along the strand. Another common sand dweller is the nocturnal sand scarab beetle. The larvae resemble oversized huhu grubs, and spend most of their time buried in moist sand feeding on rotten driftwood, and the roots of pingao and spinifex. The adults have shiny armoured wings and are clothed below in golden downy bristles. They are weak fliers due to their sheer bulk, and at dusk their plaintive droning can often be heard across the dunes. Moths and butterflies are also commonly encountered amongst the dunes. Some species of moth are entirely restricted to the dune environment. Spinifex, pingao, tauhinu and pohehue are important food sources for the larvae of both groups. Anumber of native lizards range into sand dunes throughout the country, although none are restricted in distribution solely to dunes. Our dunes support only a few native birds, unless they are adjacent to estuaries and lagoons and provide high tide roosts for a host of gulls and waders. The New Zealand pipit and banded dotterel often frequent the dunes, and can be seen racing along the strand line in search of sandhoppers and other morsels. The Australasian harrier is also a common dune resident and has been observed nesting amongst pingao. Dune country on spits and adjacent to river mouths, in Northland and Stewart Island, may sometimes support the rare New Zealand dotterel which breeds in this habitat. Threats to our natural duneland (a) Exotic conversion When Europeans began colonizing New Zealand attempts were made to stock the more extensive dune country with sheep and cattle. The livestock grazed and

trampled the sparse vegetation cover. To control the resultant large scale dune erosion European marram grass was planted throughout the country, especially on the Manawatu and eastern South Island dunes. Eventually much duneland was stabilized by dense swards of marram and converted to pasture. Extensive plantings of marram and tree lupin by the New Zealand Forest Service and private forestry companies have stabilized much natural duneland for pine plantations. Most of the Ninety Mile Beach. dunes, dunes from Kaipara harbour to Muriwai, North Canterbury dunes and some of the Manawatu sand country have been stablized and converted to exotics in this way. Because of these plantings, marram has further spread both vegetatively and by seed to become the most widespread dune plant in New Zealand. It successfully competes with pingao and spinifex in most situations, and has supplanted much of the Original vegetation. Buffalo grass and kikuyu grass in the northern half of the North Island, gorse and lupin are also capable of stabilizing dunes and displacing the natural plant cover. (b) Sand mining To date, over 35 mining and dredging operations are extracting dune sand on Crown owned land, from South Westland to Northland. Many are extracting sand from natural dune systems such as those on Kaitorete Spit, Lake Ellesmere and Kokota Spit bordering Northland’s Parengarenga Harbour. Although many of these operations are small, they are able to modify and in some cases destroy these dune systems over a relatively short period. (c) Urban and recreational development Most of the dune country close to major population centres has suffered from overuse. Reclamation of duneland for holiday houses, and damage incurred through horseriding, dune buggy and trail bike riding, have all contributed to the dunes demise. Roading construction also poses a threat to some of our natural dunelands. The recent proposal to log Waitutu forest requires the construction of a coastal access road which would pass very close

to the pristine dune country at Sandhill Point. (d) Introduced animals Damage to our dunelands by stock has been largely unchecked. Even at Te Paki Farm Park in the far north, which is managed by the Department of lands and Survey, cattle are allowed free access to otherwise unmodified dunescapes worthy of National Reserve status. At Spirits Bay cattle have almost eliminated the endangered Hibiscus (H. diversifolius) from the dunes — three plants now remain on these dunes. Rabbits and hares are also frequent browsers of our duneland plants. Although much of the foliage of adult sandbinders is unpalatable to them, they create their own special problem in that they browse seedlings instead. Browsing pressure can be so high that seedlings never establish and sandbinders must rely on less effective vegetative spread.

Natural duneland distribution today Our remaining natural dunelands are concentrated in Northland, the CascadeMartin’s Bay area, Fiordland and Stewart Island. Other areas of importance are Farewell and Kaitorete Spits, and parts of eastern Coromandel Peninsula, Manawatu and South Westland. Of dune systems that have been highly modified, the most notable are along the coastlines of the Bay of Plenty, ManawatuWanganui, north Gisborne, Chatham Islands and the dune country along most of the east coast of the South Island. One may walk along many miles of these coastlines without encountering a single native plant. Factors responsible for the decline in natural dunelands continue to operate and our natural dunelands are poorly represented in reserves. The few reserves that do support natural duneland are usually too small and often do not provide adequate protection. For example, the Kaitorete Spit Scientific Reserve, which was created to protect the Spit’s dune system encompasses but a fraction of it

and does not include the important coastal parts of the dune sequence including most of the pingaeo communities. Some dune systems are protected by sheer chance, such as those within the Farewell Spit Nature Reserve and Fiordland National park, where the main reasons for protection have been to conserve other natural values. Fortunately most of our remaining natural dunelands are on Crown owned land and could be given protective status by the stroke of a pen. However, it will also be necessary to devise management strategies to remove stock, to control introduced animals, control mining and in appropriate circumstances control the further spread of exotic weeds. Our natural dunelands have not been acknowledged as an ecosystem with conservation values equal to those of other natural areas. Steps should now be urgently taken to ensure the protection of the natural dunelands, that remain. Unless this is done we will eventually lose another part of our native heritage which contributes to New Zealand's distinctive character.

References Cheeseman, T. F. (1986): On the flora of the North Cape District. Transactions of the New Zealand Institute, 29:333. Courtney, S. P. (1983); Aspects of the Ecology of Demoschoenus spiralis. Unpublished M.Sc. thesis, Canterbury University. Tortell, P(ed) (1981): New Zealand Atlas of Coastal Resources. 60p and maps, Government Printer, Wellington. oe